This invention relates to metal matrix composites and methods of manufacturing, and more particularly, to a metal matrix composite having at least two regions that differ in composition.
Metal matrix composites are well-known materials that typically include a discontinuous particulate reinforcement phase within a continuous metal phase. An example is aluminum silicon carbide, AlSiC, which is made by infiltrating a porous, silicon carbide preform with molten aluminum.
The AlSiC metal matrix composite system has the positive attributes of high thermal conductivity, low coefficient of thermal expansion, and is lightweight. These attributes render AlSiC metal matrix composites suitable as a housing or substrate for containing or supporting electronic devices such as integrated circuit chips for which thermal conduction, coefficient of thermal expansion (CTE), and mechanical design features are important.
A negative attribute of AlSiC metal matrix composite is that it is difficult to machine via conventional milling processes because of its hardness. The milling of this material requires diamond tooling and smaller features cannot be machined because of the unavailability of small diamond milling tools. Additionally, some applications would require different coefficients of thermal expansion at different regions within or on a single, integral component. For example, some electronic devices need to be mounted on substrates with high CTE and others to substrates with low CTE. As another example, there might be a sandwich construction having a low CTE device such as an IC on one side, a high CTE substrate, such as organic board on the other side with an intermediate interlayer between them. Yet another structure is a lid covering both an IC and a substrate and is in interfacial contact with both. Previously, these needs would require separate substrates, or performance tradeoffs for a single composition component structure.
The prior art comprehended structures with a single metal matrix composite composition within a given structure that might incorporate secondary components such as substrates, seal lips, and feed-throughs. The prior art does not, however, disclose a single, integral composite component having regions with different properties.